1. Field of the Invention
This invention relates generally to the fields of molecular biology and molecular medicine and more specifically to a novel family of proteins that can regulate protein folding. The functions of these proteins are potentially diverse, including promoting tumor cell growth and metastasis.
2. Background Information
The Hsc70/Hsp70-family of molecular chaperones participate in protein folding reactions, controlling protein bioactivity; degradation, complex assembly/disassembly, and translocation across membranes. These proteins interact with hydrophobic regions within target proteins via a carboxyl (C)-terminal peptide binding domain, with substrate binding and release being controlled by the N-terminal ATP-binding domain of Hsc70/Hsp70. Hsc70/Hsp70-assisted folding reactions are accomplished by repeated cycles of peptide binding, refolding, and release, which are coupled to ATP hydrolysis by the ATP-binding domain (ATPase) of Hsc70/Hsp70 and by subsequent nucleotide exchange. The chaperone activity of mammalian Hsc70/Hsp70 is regulated by partner proteins that either modulate the peptide binding cycle or that target the actions of these chaperones to specific proteins and subcellular compartments. DnaJ-family proteins (Hdj-1/Hsp40; Hdj-2; Hdj-3) stimulate the ATPase activity of Hsc70/Hsp70, resulting in the ADP-bound state which binds tightly to peptide substrates. The Hip protein collaborates with Hsc70/Hsp70 and DnaJ homologues in stimulating ATP hydrolysis, and thus also stabilize Hsc70/Hsp70 complexes with substrate polypeptides, whereas the Hop protein may provide co-chaperone functions through interactions with the C-terminal peptide binding domain.
The Bcl-2 associated athanogene-1 (bag-1) is named from the Greek word athanos, which refers to anti-cell death. BAG-1 was previously referred to as Bcl-2-associated protein-1 (BAP-1) in U.S. Pat. No. 5,539,094 issued Jul. 23, 1996, which is incorporated herein by reference. In this earlier patent, BAG-1 is described as a portion of the human BAG-1 protein, absent the N-terminal amino acids 1 to 85. In addition, a human protein essentially identical to human BAG-1 was described by Zeiner and Gehring, (Proc. Natl. Acad. Sci., USA 92:11465-11469 (1995)). Subsequent to the issuance of U.S. Pat. No. 5,539,094 the N-terminal amino acid sequence from 1 to 85 of human BAG-1 was reported.
BAG-1 and its longer isoforms BAG-1M (Rap46) and BAG-1L are recently described Hsc70/Hsp70-regulating proteins. BAG-1 competes with Hip for binding to the Hsc70/Hsp70 ATPase domain and promotes substrate release. BAG-1 also reportedly stimulates Hsc70-mediated ATP hydrolysis by accelerating ADP/ATP exchange, analogous to the prokaryotic GrpE nucleotide exchange protein of the bacterial Hsc70 homologue, DnaK. Gene transfection studies indicate that BAG-1 proteins can influence a wide variety of cellular phenotypes through their interactions with Hsc70/Hsp70, including increasing resistance to apoptosis, promoting cell proliferation, enhancing tumor cell migration and metastasis, and altering transcriptional activity of steroid hormone receptors.
Despite the notable progress in the art, there remains an unmet need for the further identification and isolation of additional homologous BAG protein species, and the nucleic acid molecules and/or nucleotide sequences that encode them. Such species would provide additional means by which the identity and composition of the BAG domain, that is, the portion of the protein that is influencing or modulating protein folding, could be identified. In addition, such species would be useful for identifying agents that modulate apoptosis as candidates for therapeutic agents, in particular, anticancer agents. The present invention satisfies these need, as well as providing substantial related advantages.